The present invention relates to the use of compounds which contain epoxide groups and which are subjected to a heat treatment in the presence of alkylating agents as the auxiliary substances used to improve the weather resistance in the production of molded parts based on polyisocyanate polyaddition products by the reaction injection molding process ("RIM process").
The weather resistance of RIM molded parts, which are generally produced with the use of aromatic polyisocyanates, leaves much to be desired, so that their use outdoors, such as e.g. the molding material which surrounds the window panes for car windows, is not possible, although all desired mechanical properties can be provided. It is possible to lacquer the finished pane module to guarantee light protection, but this represents an additional manufacturing stage which is also very expensive.
The conventional protective agents for light and ageing represent a further possibility for the weather resistance of RIM molded bodies based on aromatic polyisocyanates. These reduce decomposition reactions by means of their chemical structure by acting as radical traps. However, these protective substances are consumed as a result of their chemical action, and a breakdown of the weather resistance is observed as soon as the auxiliary substances used are exhausted.
RIM molded parts produced from aliphatic polyisocyanates are, as a rule, considerably more weather resistant and require no additional stabilization. However, the high price of these aliphatic polyisocyanates makes their use in the large-scale production of RIM molded parts uneconomical.
It has recently been found that compounds which contain organic epoxide groups and which are subjected to heat treatment in the presence of an alkylating agent are extremely effective auxiliary substances for increasing the weather resistance of RIM molded parts based on polyisocyanate polyaddition products, particularly those based on polyurethanes which optionally contain urea groups.
Reaction mixtures based on organic polyisocyanates, and compounds which contain epoxide groups and substances with alkylating action are known for example from EP A 272,563, EP A 331,996 or EP A 368,031. In particular, according to EP A 368,031, heat treatment of the epoxide component in the presence of an alkylating agent is considered. These reactive systems of the prior publications mentioned are, however, not used for the production of molded parts by the reaction injection molding technique. In addition, there is no indication of a stabilizing action of compounds which contain epoxide groups and which are subjected to a heat treatment in the presence of alkylating agents for the purposes of the present application, as described in more detail hereinafter.